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158
Impulse radar
Impulse radar can be used to detect reinforcement, voids, pipes, etc as well as local humidity within a specimen. This
technology allows the thickness of layered structures and rebar or tendon duct positions to be relatively easy to
estimate. Very short impulse waves (< 1 ns) are sent across the concrete specimen by a tie bow or horn antenna at
frequencies typically between 500 MHz and 2.5 GHz. The impulses are then reflected back at different rates due to
the dielectric properties of the different materials within the specimen. The reflected impulses are recorded by a
second antenna.
Acoustic Methods
Acoustic methods are slower than radar but could be more reliable. This method can be used as a back up when
engineers become unsure about measurements taken by radar. A pulse is sent between two sensors with a glycerin
gel acting as a coupling agent. The pulse is either detected by the receiving sensor or by other sensors on the FRP
plate. Depth of range for this method depends on material properties: porosity, aggregate size and moisture content.
Typical depth ranges into the structure are 11.8 in to 19.7 in.
Laser Shearography
Laser speckle shearing interferometry, also known as laser shearography, is a large- area nondestructive method based
on laser interferometry. The concrete structure is covered with a relatively low intensity laser light and the image
recorded with a digital shearography camera for a reference. After heating of the structure another image is
recorded. These two images are superimposed on top of each other to determine the defects. A major advantage of
this method is that the pictures are permanent records easily used for comparisons to determine any delamination
growth over time.
9.4 National and International Codes and Installation Guidelines
The following provides review of the current national and international codes, guidelines and literature that discuss
the inspection of various FRP systems both in the field and laboratory.
American Concrete Institute
ACI 440 Committee 440 ( 2002) regulates the use of witness panels and pull- off tests to evaluate difference aspects of
an installed FRP system. It recommends that in- place load tests confirm the installed behavior of the member
strengthened with FRP. Witness panels should be used to evaluate tensile strength and modulus, hardness, lap splice
length and gel time of the FRP materials. ACI recommends that standards set forth by ASTM D 3039 and ISIS Canada

158
Impulse radar
Impulse radar can be used to detect reinforcement, voids, pipes, etc as well as local humidity within a specimen. This
technology allows the thickness of layered structures and rebar or tendon duct positions to be relatively easy to
estimate. Very short impulse waves (< 1 ns) are sent across the concrete specimen by a tie bow or horn antenna at
frequencies typically between 500 MHz and 2.5 GHz. The impulses are then reflected back at different rates due to
the dielectric properties of the different materials within the specimen. The reflected impulses are recorded by a
second antenna.
Acoustic Methods
Acoustic methods are slower than radar but could be more reliable. This method can be used as a back up when
engineers become unsure about measurements taken by radar. A pulse is sent between two sensors with a glycerin
gel acting as a coupling agent. The pulse is either detected by the receiving sensor or by other sensors on the FRP
plate. Depth of range for this method depends on material properties: porosity, aggregate size and moisture content.
Typical depth ranges into the structure are 11.8 in to 19.7 in.
Laser Shearography
Laser speckle shearing interferometry, also known as laser shearography, is a large- area nondestructive method based
on laser interferometry. The concrete structure is covered with a relatively low intensity laser light and the image
recorded with a digital shearography camera for a reference. After heating of the structure another image is
recorded. These two images are superimposed on top of each other to determine the defects. A major advantage of
this method is that the pictures are permanent records easily used for comparisons to determine any delamination
growth over time.
9.4 National and International Codes and Installation Guidelines
The following provides review of the current national and international codes, guidelines and literature that discuss
the inspection of various FRP systems both in the field and laboratory.
American Concrete Institute
ACI 440 Committee 440 ( 2002) regulates the use of witness panels and pull- off tests to evaluate difference aspects of
an installed FRP system. It recommends that in- place load tests confirm the installed behavior of the member
strengthened with FRP. Witness panels should be used to evaluate tensile strength and modulus, hardness, lap splice
length and gel time of the FRP materials. ACI recommends that standards set forth by ASTM D 3039 and ISIS Canada